TAMPA, Fla.  Republican Mitt Romney has a message for the millions of Americans who voted for Democratic President Barack Obama: It's OK to be disappointed.

The biggest moment of his political career at hand, Romney looked to appeal to the feelings of anxiety that are rippling through the electorate as the nation faces stubbornly high unemployment and fears about its future place in the world.

"Hope and change had a powerful appeal. But tonight I'd ask a simple question: If you felt that excitement when you voted for Barack Obama, shouldn't you feel that way now that he's President Obama?" Romney said as he formally accepted the Republican presidential nomination Thursday night. "You know there's something wrong with the kind of job he's done as president when the best feeling you had was the day you voted for him."

In 2008, Obama swept to victory with a message of hope and change—and as the first black person to earn the nomination of a major party, his candidacy was historic. He won in states like Virginia, Indiana and North Carolina, turning out African Americans and excited young people in record numbers.

To win, Romney needs to convince some of those voters that "hope and change" didn't really work out—and that he is the man to fix the problem.

"To the majority of Americans who now believe that the future will not be better than the past, I can guarantee you this: If Barack Obama is re-elected, you will be right," Romney said.

Aides said the speech was the most important of Romney's political career and will forever change his family's legacy. In winning his party's presidential nomination, the former Massachusetts governor has succeeded where his father failed a generation ago. But facing a two-month sprint to an Election Day matchup against President Barack Obama, Romney is now trying to broaden his appeal and connect with women and with middle-of-the road voters who will ultimately decide his fate.

To do so, he struck an often soft tone laced with deeply personal themes. He drew from Mormon faith and the influence of his mother and father—both dead for more than a decade—when he faced the Republican National Convention and a prime-time audience.

"My mom and dad gave their kids the greatest gift of all—the gift of unconditional love. They cared deeply about who we would be, and much less about what we would do," Romney said.

George Romney, a Michigan governor, ran for the Republican presidential nomination in 1968 when Romney was a young man. His mother, Lenore, ran unsuccessfully for the U.S. Senate in Michigan in 1970.

The entire evening—from the physical staging to the speakers' program to the planned whole-family entrance after Romney's big speech—was aimed at introducing the sometimes stiff and distant politician as a businessman, Olympic savior and deeply religious family man. His pitch to his party, as well as to the many undecided voters who are disappointed in the country's direction, will be that he's the candidate better able to shoulder the country's economic burdens.

Clint Eastwood had the honor of whipping up the crowd ahead of Romney's speech.

The iconic star of "Dirty Harry" criticized Obama for failing to turn the economy around and for wanting to close the Guantanamo Bay prison for terror suspects.

Eastwood said Obama has failed to deliver on his promises and it's time for Romney and his running mate, Paul Ryan, to take over.

He entertained the audience with a mock interview with Obama, posing questions and pretending that Obama had told Eastwood to shut up.